Baking cloth simulation use only 20% of cpu ressources, how to get 100%?
Do you have a quad core? Simulation calculations are not multithreaded, and so cannot use more than 1 core at once. If it's using up a single core of your quad core, that'd be your 20-25%. There is no way to increase this unless someone gets a multithreaded physics algorithm into blender (these exist, but they are complicated and there are caveats. The program Marvelous Designer has multi core cloth sim, and maybe some other expensive programs.)

However, you could run multiple entirely separate physics bakes, or bake physics while rendering or performing other tasks.